Vacuum tube and its elements



Oct. 20, 1931.

S. RUBEN VACUUM TUBE AND ITS ELEMENTS Filed Aug. 26, 1927 awuemtoz SAMUEL RUBEN 33x 111$ 6111mm; Wk/4% Patented Oct. 20, 1931 SAMUEL RUBEN, or form, '1 i.Y., assrGnon'ronUBE-N TUBE-COMPANY, noonroaa'rIoN or DELAWARE V vnc'ouivr rurn'enn rrs ELEMENTS:

Application filed-August as, 1927. Serial no. 2153753.

This invention relates to a vacuum tube and more particularly to a vacuumtube uti lizing alternating current for ,rheatinglthe cathode and to the elements thereof.

The chief object of the invention is to pro Vide a vacuum tube operating upon an alter? nating current circuit having high thermal efficiency with a minimum thermal lag. v

In addition to'having a high thermionic efliciency, a'vacuum tube must be; prompt in its response to the application of the alternating current; that is, the-thermal lag must be a minimum in that the time elapsing be.- tween the application of the cathode heating or alternating current and the time when there is sufficient, electron emission from the cathode elementmus't be brief to be practicable. The tube of my present invention employsa heating element contacting with an electrically conductive element of higher specific resistance, which is-in surface contact with a cathode elementhaving asurface capable of copious electron emission. i

In a preferred form of construction of the tube of my present invention, agraphite member or rod is used as the electrically conductive element-of relatively high specific resistance; upon thisv the heater wire or ele-. ment in the alternating. current circuit :is wound; also uponthe .conductivemember, but not contacting with the-heater wire, in surface contact therewith, is the cathode ele ment which has a. surface'of high electro emissivity.

The graphite rod is spirally threadedlso that a shallow groove is spirally out along its cylindrical surface in which the heater wire fits just below the surface of the rod. A thin nickel tube, with its outer surface coated with an oxide of an alkaline earth, such as barium or strontium, or a mixture of both, is placed in surface contact with the carbon rod.

Due to the good thermal conductivity of the graphite or carbon rod and the shunt path between the heater element and the nickel cylinder, the cathode is rapidly raised to thermionic emission temperature.

As the conductive graphite rod separates the heater wire from the nickel cathode cylinder,.there is a leakage current through the rod fromopposite ends of the heatingzfilament which assists in heating the cathode and V tendsto stabilize the temperature and reduce thermal fluctuations due to line variations,

and to reduce the alternating current noise or hum by. reducing the intensity of the electri cal field produced by the heating current.

It is-desirable, of course, to employ in any electron emission tube a cathode having a high degree ofemissivity at relatively low temperatures. I have obtained the best results by applying to a suitable cathode metal base, in-this case the nickel cylinder, an ale kaline earth coating composedof equal parts by weight of barium and strontium oxides finely groundvand thoroughly mixed with one tenth of the total weight of powdered resin; to the three constituents is added a. resin solvent until the whole forms a suitable paste. Before applying the paste the nickel surface is preferably oxidized, the oxide on being heatedin contact with the mixture being alkaline earth oxides and the nickel surface. I

WVhen'the mixture has beenfapplied in any suitable manner to the oxidized nickel surface and has been air dried, the whole is baked to aboutQOO? centigrade, af;ter which the resin is burnedout, 7-

My experiments have shown that a high electron emission is obtained from such a cathode at a temperature materially lower than by cathodes coated with alkaline earth compounds bythe methods-known to the art; and further, Ihave found that any substantial deviation from the above formula for the mixture yields a materially lower efficiency. The intimate'surfacecontact of a very thin coating of the alkaline earth oxides the nickel minimizes the thermal and electrical resistance of the element, and thercf0re,the requisite cathode metal temperature.

-A-.1cathode made in accordance withthe cathode heater and other elements contained;

Fig. 2 the conductive rod of graphite, which is one-sixteenth of an inch in diameter and has a resistance of 100 ohms per longitudinal inch and is superficially threaded (five threads to the inch) to a depth of about .006 inch. Fig. 3 represents a section plan view of the tube and its elements.

At 1 is a nickel cathode element coated with a mixture containing strontium and barium oxides, 2 the anode cylinder having therewithin the wire grid 3. The cathode is supported by conductive rods 1a and 1b; the anode 2 is supported by rods 2a and 2b and the grid 3 by rod 3a. The rods 1a, 2a and 3a are adapted for connection in an electric circuit. Spirally wound on the surface of a graphite rod 5 is the heater wire, lying within a groove below the surface. The spirally wound heater wire of tungsten is supported and adapted for connection in the heater circuit by rods 40. and 4b. The cathode cylinder 1 fits closely upon the graphite rod 5, but not in contact with theheater wire 4 wound in the groove on the surface of carbon rod 5. The oxide coating on the nickel cylinder 1 is previously coated with the mixture made of powdered barium and strontium oxides with resin and a resin solvent to effect the copius emission of electrons, which occurs at relatively low temperatures to the anode 2,

the electron stream being controlled by the grid element 3 between the cathode and anode. While the graphite or carbon is considered preferable for the heater element base and as a separator between the heater Wire and the cathode, other electrically conductive materials having resistances higher than the heater elements, to limit leakage currents, can be used, such as metallic alloys of chromium and metallic compounds of carbon.

VVhat-I claim is:

1. A sealed evacuated envelope containing, a cathode, an anode, a grid and a heater element for indirectly heating the cathode to emission temperature, comprising a conductive filament mounted in a groove adjacent the periphery of a conducting member having a specific resistance higher than that of said conductive filament.

2. A sealed evacuated envelope containing, a grid, an anode, an indirectly heated cathode having a coating of alkaline earth oxides and a heater element for heating the cathode to emission temperature, comprising a conductive filament mounted upon a conductive member havin a specific resistance higher than that of said conductive filament.

3. A sealed evacuated envelope containing, a cathode, an anode, a grid and means for heating the cathode to emission temperature, comprising a conductive element mounted upon a graphite rod.

4. A sealed evacuated envelope containing,

a grid, an anode, a cathode having a coating of alkaline earth oxides and means for heating the cathode to emission temperature, comprising a conductive element mounted upon a graphite rod, said cathode also being mounted upon and in surface contact with said graphite rod.

i 5. A sealed evacuated envelope containing, a cathode, an anode, a grid and a heater element for indirectly heating the cathode to emission temperature, comprising a conductive filament mounted upon a conductive member having a specific resistance higher than that of said conductive element, the cathode also being mounted upon and in surface contact with said conductive member.

6. A sealed evacuated envelope containing a cathode, an anode, a grid and a heater element for indirectly heating the cathode to emission temperature, said heater element comprising a conductive filament mounted on a. graphite member in a helical groove adjacent the periphery of said member.

7. A sealed evacuated envelope containing a cathode, an anode, a grid and a heater element for indirectly heatin the cathode to emission temperature, sai heater element comprising a conductive filament mounted in a helical groove adjacent the periphery of a graphite member, the cathode being in surface contact with said member, but not in contact with said heater element.

8. A sealed evacuated envelope containing an indirectly heated cathode having a coating of barium and strontium oxides, an

anode, a grid and a heater element for heating the cathode to emission temperature, said heater element comprising a conductive element, mounted on a graphite member in a helical groove adjacent the periphery of said member.

In testimony whereof, SAMUEL R BEN has signed his name to this specification this 25th day of August, 1927.

SAMUEL RUBEN. 

